Jump to content
Brian Enos's Forums... Maku mozo!

Mysterious overpressure


BoyGlock

Recommended Posts

Let me clear the air. As the title says I acknowledge the over pressure. Theres no doubt about that. I also know the risks and dangers of this. What Im after is the cause as there should not be pressure problem from my data except the increased crimp which to me still did not jibe with the resultant problem encountered. Which led me to investigate everything and discovered a crack in my powder measure. Still Im studying this crack if and how this made the powder charge excessive.

Ive just loaded another 200 rnds with same 10grn ziira 7 but in different powder measure. This one metered consistently from day 1. Will chrono later and update this thread. 

Thanks for everyone's concern. 

Link to comment
Share on other sites

  • Replies 57
  • Created
  • Last Reply

Top Posters In This Topic

Did you pull any bullets from the first batch and weigh the charges?

 

Like Jack said, every powder has a point past which more powder yeilds less velocity, you could be over the hump getting 170pf on the way back down.

 

You already back off the crimp which I think will help, but I also recommend loading ten each at 9.0, 9.2, so on up to 10.2 and running them over the chrono.

Link to comment
Share on other sites

Finally, chrono data made sense. 10gn of Z7 yielded 169pf in unported comped kkm barrel, 166 in ported/hibrid schuemann comped barrel. The cracked powder measure should be the culprit. Still have to see how it affected the powder throw. 

 

kneelingatlas, I already did those checks before I discovered the cracked powder measure and had mixed illogical results. 

 

Now, to the cause of that crack, I posted a comment about it in a thread in Dillon Equipment forum here. 

 

Thanks everyone. 

Link to comment
Share on other sites

Crimp is not crimp, it's just a de-belling step, only enough to get it to case gage, which is only a few thousands. I don't measure at all, but use a permanent marker to see how far down the die is going on the round (course if varies slightly for each case of different head stamp) until it just drops in the case gage.

 

image37113.jpg

 

 

Link to comment
Share on other sites

I would say that when you had to "adjust" powder throw repeatedly across a hundred you over charged some.

 

Different  results means danger. Especially with a powder that seems to be quite fast burning.

 

Hope you stay safe after fixing the root cause.

Link to comment
Share on other sites

I'm curious about the crimp data that was posted. You mentioned crimping to .369 and then "opening it up" to .375.

 

Both of those numbers seem overly tight to me. I typically try to get my crimp at .378/.379. If I saw multiple crimps less than .377 I'd probably tweak it up a bit.

 

I only load 9mm minor so maybe 9mm major protocol is different?

Link to comment
Share on other sites

Trying to measure the very, very, tip edge of the brass where the brass & crimp end is pretty iffy. I do not trust that method at all.

Better is to just eyeball the cartridge, while adjusting lighting and reflection off the brass, looking for a very slight contour inwards. Hard to see if there is a little "too much" crimp like this, but you can definitely see "not enough".   

 

Best way I found to reliably measure correct crimp is this:

1- measure bullet diameter (.355 in example picture)

2- pull a bullet from cartridge you just loaded

3- look for a very slight indentation ring in the bullet where the tip of the crimp was (tip of knife in picture).

4- measure bullet diameter at the crimp ring (.353 in example picture)

 

My experience is that this is best if .001-.003 less than full diameter measure (I.e. .355 - .353 = .002 ).

This method is 100% repeatable; just need a bullet puller.

 

crimp-1.jpg

crimp-2.jpg

crimp-3.jpg

Link to comment
Share on other sites

I admit mine is a bit over crimped at .375". I used to just remove the bell in the case mouth to avoid deforming the bullet for accuracy but I experienced intermittent ftf accross 3 of my 2011s in .38sc. Not so frequent but usually comes in the most crucial matches. Recently it became a bit more frequent. A clubmate who also reloads his own .38sc noticed my dilemma and suggested to try increasing my crimp. I did and to this date I still have to see that ftf again after about 500 rnds. 

Measuring crimp at the very mouth of the shell is a bit hard to be consistent. But it can be done. I do it just for comparison. I agree eyeballing it is good enough as I do it most of the time. But somebody here opined strongly against it so I took the measurement and posted it here. Otherwise Im ok how it looks. 

Link to comment
Share on other sites

1 hour ago, BoyGlock said:

I admit mine is a bit over crimped at .375". I used to just remove the bell in the case mouth to avoid deforming the bullet for accuracy but I experienced intermittent ftf accross 3 of my 2011s in .38sc. Not so frequent but usually comes in the most crucial matches. Recently it became a bit more frequent. A clubmate who also reloads his own .38sc noticed my dilemma and suggested to try increasing my crimp. I did and to this date I still have to see that ftf again after about 500 rnds. 

Measuring crimp at the very mouth of the shell is a bit hard to be consistent. But it can be done. I do it just for comparison. I agree eyeballing it is good enough as I do it most of the time. But somebody here opined strongly against it so I took the measurement and posted it here. Otherwise Im ok how it looks. 

 

 

If you're not chamber checking your match ammo, I strongly suggest you start.  You can easily do 100% of your match ammo the night before sitting in front of the TV, takes me about an episode of the Walking Dead

Link to comment
Share on other sites

4 hours ago, BoyGlock said:

I admit mine is a bit over crimped at .375". I used to just remove the bell in the case mouth to avoid deforming the bullet for accuracy but I experienced intermittent ftf accross 3 of my 2011s in .38sc. Not so frequent but usually comes in the most crucial matches. Recently it became a bit more frequent. A clubmate who also reloads his own .38sc noticed my dilemma and suggested to try increasing my crimp. I did and to this date I still have to see that ftf again after about 500 rnds. 

Measuring crimp at the very mouth of the shell is a bit hard to be consistent. But it can be done. I do it just for comparison. I agree eyeballing it is good enough as I do it most of the time. But somebody here opined strongly against it so I took the measurement and posted it here. Otherwise Im ok how it looks. 

 

Wow, I had almost the same experience!

I adopted my current crimping technique after multiple seemingly random FTF's in in my 38SC culminated my frustration at 2010 Nationals. My gunsmith suggested I tighten up the crimp a little (1/12 turn) and I noticed when I pulled the bullet it left an indentation ( measured .353). Have not experienced that problem again since. I shoot 6" steel at 50 frequently and groups as well from time to time to verify zero. Accuracy is absolutely NOT affected ( at least not with the MG JHP's I use).

 

I understand that way too much crimp reduces the hold of brass on the bullet, but I don't believe this is any factor with the level of crimp I am using. It takes a very solid blow with the kinetic puller to eject the bullet from case.

 

Any other reasons a very slight indentation in bullet may be a bad idea?

Link to comment
Share on other sites

This ziira 7 powder leaves nasty stains in the brass that cant be removed by dry tumbling even with a tinge of liquid polish sprinkled on media. I dont do wet tumbling so I just let it be. Those are 2-3x fired brass thats tumbled for an hour+ for every usage. 3n37 3n38 donot have such stains. But muzzle flip-wise, ziira 7 has very noticeable edge over those vihta powders. We dont have other powders for open gun loads that i know of and that i can compare in my country. 

 

Eta. And 3n37 costs 77% more and 3n38 138% more than z7 here. 

Edited by BoyGlock
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



×
×
  • Create New...